SSC Science 2026 Excretion for CGL, CHSL, CPO & MTS

Excretion is the biological process of eliminating toxic metabolic waste products from the body. These waste products, including urea, carbon dioxide, and excess salts, are produced during metabolic activities and, if accumulated, can be harmful to the body. 

The process helps maintain internal balance and homeostasis. In humans, excretion occurs through organs like the kidneys, lungs, and skin. Proper excretion is crucial for overall health and well-being. This topic is essential for SSC Science 2026, especially for CGL, CHSL, CPO, and MTS exams, as it is a key part of the SSC CGL Biology Excretion syllabus.

SSC Science 2026 Excretion

The body generates various waste products through metabolism. Excretion removes these wastes to maintain internal balance (homeostasis). The primary excretory products include urea, uric acid, carbon dioxide, and excess water.

Excretory Products

Different organisms produce different nitrogenous waste products. Their type depends on water availability.

Human Excretory System

The human excretory system, also known as the urinary system, consists of several organs working together. This system is key for SSC Excretion 2026 preparation.

• Kidneys: A pair of bean-shaped organs. They filter blood and produce urine. Kidneys are located on either side of the backbone.

• Ureters: A pair of tubes connecting each kidney to the urinary bladder. They transport urine from the kidneys.

• Urinary Bladder: A muscular sac that stores urine temporarily. Its capacity is around 300-500 ml.

• Urethra: A tube that carries urine from the bladder out of the body.

Nephron: Functional Unit of Kidney

Each kidney contains about one million nephrons. Nephrons are the structural and functional units of the kidney. They perform the actual filtering of blood.

• Structure: Each nephron has a glomerulus and a renal tubule. The glomerulus is a tuft of capillaries. The renal tubule is a long, convoluted tube.

• Function: Nephrons filter blood, reabsorb useful substances, and secrete waste. This leads to urine formation.

Urine Formation

Urine formation involves three main steps within the nephron. This mechanism is central to the SSC CHSL Science Excretion topic.

1. Glomerular Filtration: Blood enters the glomerulus under high pressure. Water, salts, glucose, amino acids, and urea filter from the blood into Bowman's capsule. Large proteins and blood cells do not filter.

2. Tubular Reabsorption: As the filtrate moves through the renal tubule, useful substances are reabsorbed. Glucose, amino acids, much water, and some salts return to the blood. This process is selective.

3. Tubular Secretion: Waste products like excess potassium, hydrogen ions, and some drugs are secreted from the blood into the tubule. This maintains pH balance.

Other Excretory Organs

While kidneys are primary, other organs also help remove waste. This broader view is important for SSC CPO Science Syllabus.

• Lungs: Remove carbon dioxide and water vapor during respiration.

• Skin: Excretes excess water, salts, and a small amount of urea as sweat.

• Liver: Breaks down old blood cells, deaminates amino acids to form urea, and excretes bile pigments.

Excretion in Plants

Plants also excrete waste products. They use different methods than animals.

• Stomata: Release oxygen, carbon dioxide, and water vapor.

• Storage: Store waste in leaves that fall off.

• Resins and Gums: Store waste products in bark and old xylem.

Key Mechanisms of Excretion

The primary mechanism is urine formation in the human kidneys. This process ensures the body's internal environment remains stable.

Mechanism of Urine Formation

The kidneys meticulously form urine to filter blood and remove toxins. This involves a coordinated effort of filtration, reabsorption, and secretion.

1. Afferent Arteriole: Brings blood to the glomerulus.

2. Glomerulus: Filters blood based on particle size and pressure. This forms the glomerular filtrate.

3. Bowman's Capsule: Collects the filtered fluid.

4. Proximal Convoluted Tubule (PCT): Reabsorbs most of the useful substances. These include glucose, amino acids, and vital salts.

5. Loop of Henle: Creates a concentration gradient in the kidney. This helps in water reabsorption.

6. Distal Convoluted Tubule (DCT): Further reabsorption of water and salts occurs. It also secretes hydrogen and potassium ions.

7. Collecting Duct: Collects urine from many nephrons. It adjusts water content based on body needs.

8. Ureters, Bladder, Urethra: Transport and expel the final urine.